Hi - me again!
Ok, I think I mentioned that I was going to bin my 'magnets & reed switch'...in favour of an optical pickup (I needed more 'resolution' & less debouncing) - well, I have all the pieces in place now...so why am I back?
well, I need help wrt how I can be sure to ascertain that my circuit (& program) is actually picking up all the pulses fine. And with a motor turning at between 300 & 400RPM, and 48 stripes per revolution...I lose count when doing this manually!
Here's the circuit I've implemented.... http://hans-w.com/RPM.gif (I should point out that Im not using the same PIC - I'm using a 16F690 - nor his hex code...as I need to be able to customize the program)
Re the tach pickup itself - on the edge of my turning motor is a phototransistor aimed at a round disc with 48 lines on it (essentially a pie chart knocked up in Excel, printed onto a CD label & then onto an old CD!!) ...as each one of these lines passes the phototransistor, a pulse ultimately appears at a PIC input pin.
It seems to be working reasonably well *but* I have a sneaking suspiscion, that either the electronics is not setup right (there's a preset in that schematic that needs setting optimally - I have a scope, but at 48 pulses per rev running at 400RPM, the trace is too jittery to set the levels in this manner).
What I'd like to know, is the best way to establish that *all* 48 stripes are being 'seen' by the PIC and everyrevolution (not just for one revolution, but say over 400 revolutions).
I'm figuring it'll need some form of counter, with the methodology being something along these lines (this is a labourious method!)....
Start counter
Pulse 1 arrives - output this info to screen along with counter time (I'm using the Pickit2 Uart tool to debug)
Pulse 2 arrives - output this data to screen along with counter time.
I can then cut/paste the above into Excel, do a bit of simple maths (ie subtract each 'counter time' from the previous, which will yield the time taken beteween successive pulses) & ultimately put this into a bar chart. All being well my bar chart should have bars of equal height from left to right.
Since the above method seems a bit long winded, I'm sure there must me a slicker way in real time, for example...
Start counter
Pulse 1 arrives - note the time in variable1
pulse 2 arrives - note the time in variable2
Subtract variable 1 from variable 2 (to give the time between pulses) - place into variable 3
then continue in a similar vein?
The clever bit would be to have a calculation that goes along the lines of "If the time between successive pulses is greater than say 90%, then we must have missed a pulse - output this info to screen via the Pickit Uart tool.
Does this sound plausible?
Could anyone help me out with a little bit of code to get me started please?(I've never dealt with counters previously!)
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